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When referring to this work, full bibliographic details including the author, title, awarding institution and date of the thesis must be given e.g. AUTHOR (year of submission) "Full thesis title", University of Southampton, name of the University School or Department, PhD Thesis, pagination http://eprints.soton.ac.uk UNIVERSITY OF SOUTHAMPTON FACULTY OF NATURAL AND ENVIRONMENTAL SCIENCES Chemistry DEVELOPMENT OF RESONANT INELASTIC X-RAY SCATTERING SPECTROSCOPY FOR 4d AND 5d TRANSITION METAL CATALYSTS Rowena Thomas Thesis for Degree of Doctor of Philosophy APRIL 2013 UNIVERSITY OF SOUTHAMPTON ABSTRACT FACULTY OF NATURAL AND ENVIRONMENTAL SCIENCES Chemistry Doctor of Philosophy DEVELOPMENT OF RESONANT INELASTIC X-RAY SCATTERING SPECTROSCOPY FOR 4d AND 5d TRANSITION METAL COMPLEXES By Rowena Thomas This research focuses on the development of Resonant Inelastic X-ray Scattering spectroscopy (RIXS) as a tool in homogeneous catalysis for 4d and 5d transition metals. In the RIXS data 2D plots of x-ray emission spectra as a function of absorption were obtained, showing the relationship between the two techniques as well as probing both the unfilled and filled DOS. They also provided L edge spectra with greatly reduced lifetime broadening. Previous studies have shown the L-edge x-ray absorption near edge structure (XANES) to be sensitive to the oxidation state and geometry, but the origins of spectral features are not always well understood. The aim of this work was to use RIXS to gain a more detailed understanding of these features and the electronic and geometric information that can be deduced from the spectra. Molybdenum core to core RIXS data for a series of reference compounds was successfully analysed with the help of simulations using an extension of FEFF9. This showed the potential for the use of RIXS in determining more accurate oxidation states and deriving information about the geometry. Crystal field splitting parameters could be extracted directly from the dd band splitting observed. Novel high energy resolution XANES and valence band RIXS data has been obtained for a series of tungsten and rhenium reference compounds, and the spectra have been simulated using an extension of the FEFF9 multiple scattering code. Clear trends in the incident energy and energy transfer position can be seen as a function of oxidation state and ligand type. This information was then applied to interpret the VB RIXS obtained on a homogeneous tungsten dimerisation catalyst, and used to provide insights into the oxidation state and ligand type of the catalytic intermediates before, during and after catalysis. ACKNOWLEDGEMENTS The last four and a half years have been full of highs and lows; I couldn’t have got through this time without the help of my friends and colleagues. Firstly I would like to thank my supervisor Moniek Tromp for all her support, advice, opportunities and encouragement over the course of my PhD, it has been a pleasure to work with you. I would also like to thank Andreas Danopoulos for all his help and supervision during the first two years of my PhD, thank you for making lab work so fun and for sharing your passion for Chemistry. I would also like to thank John Evans for all of his helpful advice and support. I am grateful for all the help and advice from different collaborators and beamline staff during the course of my PhD. I would like to thank Josh Kas for all his invaluable assistance with the FEFF calculations and discussions on the related theory. I would also like to thank Pieter Glatzel, John Rehr and Frank de Groot for their useful input on RIXS theory. For all their help with the HERFD and RIXS experiment I would like to thank the staff at ID26, ESRF, in particular Pieter Glatzel, Janine Grattage and Kristina Kvashnina. Thanks to Evgueni Kleimenov for assistance at the SLS. I would like to thank all the members of the Tromp/Evans group during my time at Southampton. In particular I would like to thank Sarah Hobbs for being an incredibly helpful colleague and a wonderful friend. It made all the difference to have someone to share the pain and make beamtimes fun! To Peter Wells I genuinely appreciate all the advice, encouragement and inappropriate humour over the years. Thank you to Stuart Bartlett for all the help on beamtimes and for always making the office more fun when you were around! In addition thank you to Khaled Mohammed and Michal Perdjon-Abel for all your kind words and encouragement. Elsewhere in the Chemistry department there are a number of people I am grateful to, but especially the following. Thank you to Paolo Farina for being generally wonderful and providing much tea and hugs in stressful times. Christianne Wicking thank you for being an amazing friend and for always being right. Sophie Benjamin thank you for always brightening up my day! Thanks to Susana Conde-Guandano, Alan Henderson, David Bolien and Cyril Henry for making the lab so much fun (and so efficient!) in my first two years. Finally I would like to thank my parents and my favourite sister for all their love and support, for always believing in me, and for knowing not to ask when I would finish this thesis. Glossary of Terms Techniques XAS X-ray Absorption Spectroscopy XES X-ray Emission Spectroscopy XAFS X-ray Absorption Fine Structure EXAFS Extended X-ray Absorption Fine Structure XANES X-ray Absorption Near Edge Structure RIXS Resonant Inelastic X-ray Scattering VB RIXS Valence Band Resonant Inelastic X-ray Scattering DFT Density Functional Theory LDOS Local Density of States DOS Density of States MS Multiple Scattering MO Molecular Orbital NMR Nuclear Magnetic Resonance Spectroscopy IR Infrared UV/vis UV- visible General ν Vibrational frequency λ Wavelength Hz Hertz δ Chemical shift ppm Parts per milliion s Singlet d Soublet t Triplet m Multiplet fac Facial mer Meridional Me Methyl Et Ethyl Bu Butyl Ph Phenyl Ar Aromatic o ortho TABLE OF CONTENTS Chapter 1: Introduction 1.1 Overview of project 1 1.2 Catalysis 3 1.2.1 Overview 3 1.2.2 Polymerisation of alkenes 5 1.2.3 Tungsten imido catalyst for selective dimerisation of low 7 molecular weight alkenes 1.3 XAFS techniques in catalysis 12 1.3.1 Practical developments 12 1.3.2 Theoretical considerations 14 1.4 References 16 Chapter 2: X-ray Techniques 2.1 Introduction 19 2.2 X-ray Absorption Spectroscopy 19 2.2.1 X-rays and the Photoelectric Effect 19 2.2.2 Synchrotrons and Beamlines 20 2.2.3 Detection methods 23 2.2.4 X-ray Absorption Fine Structure Spectroscopy 25 2.2.5 Extended X-ray Absorption Fine Structure (EXAFS) 28 Spectroscopy 2.3 X-ray Absorption Near Edge Structure 30 2.3.1 Introduction 30 2.3.2 Multiplet effects 30 2.3.3 Studies of K-edge XANES 31 2.3.4 L-edge XANES 32 2.3.5 Molybdenum XANES 33 2.3.6 Tungsten and rhenium XANES 35 2.3.7 Energy resolution of XANES 36 2.3.8 High Energy Resolution Fluorescence Detected XANES 36 2.4 X-ray Emission Spectroscopy 37 2.5 Resonant Inelastic X-ray Scattering 40 2.5.1 Introduction 40 2.5.2 The RIXS process 41 2.5.3 Valence Band RIXS 44 2.6 Data Analysis 45 2.6.1 Summary 45 2.6.2 FEFF9 46 2.7 References 47 Chapter 3: Experimental 3.1 Introduction 53 3.2 Instrumentation and general techniques 53 3.3 Synthesis of tungsten reference compounds 54 3.3.1 WOCl 4 54 3.3.2 WCp*Me 4 54 t 3.3.3 WCl 4N(4- BuPh) 55 3.4 Synthesis of rhenium reference compounds 3.4.1 [Re(o-pda) 3][ReO 4] 56 3.4.2 Re(o-pda) 3 56 3.5 Tungsten imido catalysis 56 3.6 RIXS experiments 57 3.6.1 Experimental set-up December 2009 (ESRF) 57 3.6.2 Experimental set-up December 2010 (ESRF) 58 3.6.3 Experimental set-up July 2011 (ESRF) 58 3.6.4 Experimental set-up July 2010 (SLS) 59 3.6.5 Sample preparation – powders 59 3.6.6 Sample preparation – solutions 59 3.7 FEFF9 calculations 59 3.7.1 Overview 59 3.7.2 FEFF parameters for Mo L α RIXS calculations 60 3.7.3 FEFF parameters for W and Re L 3 valence band RIXS 62 calculations 3.8 References 67 Chapter 4: Molybdenum Reference Studies 4.1 Abstract 69 4.2 Introduction 69 4.3 Experimental 73 4.4 Results 75 4.5 Discussion 81 4.6 Conclusions 83 4.7 Notes 83 4.8 References 84 Chapter 5: Tungsten Reference Compounds 5.1 Introduction 87 5.2 Tungsten (IV) oxide 88 5.3 Tungsten (VI) oxide 93 5.4 Lithium tungstate 97 5.5 Tungsten (VI) oxotetrachloride 99 5.6 Tungsten hexacarbonyl 103 5.7 Bis(tert-butylamido) bis(tert-butylimido) tungsten 107 5.8 Pentamethylcyclopentadienyl tetramethyl tungsten 110 5.9 Dimethoxyethane dichlorodioxo tungsten 113 5.10 WCp*Cl 4 116 5.11 Tungsten hexachloride 117 5.12 Discussion and comparison of Valence Band RIXS 118 5.13 L beta 2 RIXS for tungsten reference compounds 120 5.14 Conclusions 122 5.15 References 124 Chapter 6: Rhenium Reference Compounds 6.1 Introduction 125 6.2 Rhenium (IV) oxide 125 6.3 Rhenium (VI) oxide 129 6.4 Mer - trichlorotri(methyldiphenylphosphine) rhenium 133 6.5 Trichlorooxobis(triphenylphosphine) rhenium 136 6.6 Rhenium tris(o-phenylenediamide) 139 6.7 Summary 142 6.8 Conclusions 143 6.9 References 143 Chapter 7: Tungsten Catalysis 7.1 Introduction 145 7.2 Experimental results – VB RIXS 147 7.2.1 Experimental L 3 VB RIXS spectra 147 7.2.2 Summary table of experimental L 3 VB RIXS results 150 7.3 Experimental results – HERFD reactions 152 7.4 Other experimental results 155 7.4.1 Precursor vs.

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